Magnetic development units

ABSTRACT

To improve magnetic brush and magnetic transport cascade-type development units for electrostatic copiers and the like, there is a resilient baffle for suppressing uncontrolled emissions of toner while leveling the profile of the magnetically entrained developer material.

United States Patent 1191 Howard et al.

MAGNETIC DEVELOPMENT UNITS inventors: Willard L. Howard, Marion;

Thomas A. Tietjen, Rochester, both of NY.

Xerox Corporation, Stamford. Conn.

Filcd: May 28, 1974 Appl. No.: 473,651

Assignee:

US. Cl. 118/637 Int. Cl. G03G 15/08 Field of Search 118/637, il7/l7.5

Relerences Cited UNiTED STATES PATENTS 3/l960 Oldenboom 8/637 1 Nov. 25,1975 3,428,025 2/l969 Sullivan, Jr. ll7/i7.5 3,572,289 3/1971 3,64l,9802/1972 3,649,262 3/l972 3,724,422 4/1973 Latone et al 1 18/637 PrimaryExaminer-W. C. Reynolds Assistant Examiner-Douglas Salser [57] ABSTRACTTo improve magnetic brush and magnetic transport cascade-typedevelopment units for electrostatic copiers and the like. there is aresilient baffle for suppressing uncontrolled emissions of toner whileleveling the profile of the magnetically entrained developer material.

7 Claims, 4 Drawing Figures Sheet 1 of 2 US. Patent Nov. 25, 1975 U.S.Patent Nov. 25, 1975 Sheet 2 of FIG. 3b

MAGNETIC DEVELOPMENT UNITS BACKGROUND OF THE INVENTION This inventionrelates to development units forielec-j trostatic copiers andduplicators (hereinafter collectively referred to as copiers") and. moreparticularly.

" substantially full width. flexible baffles are included in to meansfor suppressing uncontrolled'emissions off toner from development unitsfor continuous copiers.

In a conventional electrostatic copying process of the type disclosed inCarlson U.S. Pat. No. 2.297.691 on Electrophotography." a uniformlycharged photoreceptor is selectively discharged in an imagewiseconfiguration to provide a latent electrostatic image which issubsequently developed by means of a finely divided, lightweight.electroscopic marking material, called "toner." This process has enjoyedoutstanding commercial success. especially in continuous copiers.Nevertheless. substantial effort and expense are still being devoted tothe perfection of development units for applying the toner on the fly asthe photoconductor moves through a development zone.

Magnetic brush and magnetic transport cascadetype development units haveboth shown substantial promise for use in continuous copiers. Theyemploy a developer material which normally includes triboelectricailycharged toner in combination with a relatively coars. granular magneticmaterial. such as ferrite beads. In operation; the magnetic componentcarries the toner from a sump to the development zone where toner iselectrostatically stripped from the. magnetic carrier to develop thelatent image. Thereafter the partially denuded carrier is returned tothe sump for recirculation.

Continuity is achieved by adding new toner to the sump from time-to-timeto replace the toner consumed in the development process. Preferably.the additional toner is added automatically while the copier is inoperation. However. it has been found that there sometimes areuncontrolled. powder cloud-like emissions of toner from the toneraddition regions of magnetic brush and magnetic transport cascade-typedevelopment units due to the air currents generated by the motion of thephotoconductor. developer. and developer transport system.Unfortunately. those emissions have the undesired effect of increasingthe background development levels of the ultimate copies.

SUMMARY OF THE INVENTION Accordingly. an object of this invention. is toprovide means for suppressing uncontrolled emissions of toner fromdevelopment units for electrostatic copiers. More particularly. anobject is to provide means for containing airborne particles of tonerwithin such a development unit.

Even more specifically, an object of the presentinvention is to providea self-sealing baffle for suppressing uncontrolled emissions of tonerfrom magnetic brush and magnetic transport cascade-type developmentunits for continuous copiers. A more detailed object is to provide ab'affle which not only accomplishes that function. but which alsoimproves the uniformity of the development process by aiding in levelingthe profile of the magnetically entrained developer mate'- rial.

Another object of this invention is to provide a reliable and relativelyinexpensive self-sealing baffle for carrying out the above-mentionedfunctions in new and the' .ill ustrated magnetic brush and magnetictransport cascade-type developme'nPunits. Each of the baffles "II88on'e'side anchored tq the housing for the developer unit andits'opposite. free side biased into engagement with the magneticallyentrained developer material. Preferably. the free sides of the bafflesare arcuate so that each of them presents a continuous. edge free.contact surface for leveling the profile of and seating against thedevelopment material without any appreciable scraping action.

BRIEF DESCRIPTION OF THE DRAWINGS Still further objects and advantagesof the present invention will become apparent when the followingdetailed description is read in conjunction with the attached drawings,in which:

FIG. 1 is a fragmentary. sectional view of a continuous electrostaticcopier including a magnetic brush development unit embodying the presentinvention;

FIG. 2 is another fragmentary, sectional view of a continuouselectrostatic copier including a magnetic transport cascade-typedevelopment unit embodying the present invention;

FIGS. 3A and 3B are schematic views illustrating the profile of themagnetically entrained developer on the upstream side and the downstreamside. respectively. of the baffle in the development unit shown in FIG.1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS While the inventionis described in some detail hereinafter with specific reference tocertain embodiments. it is to be understood that the intent is not tolimit it to those embodiments. On the contrary, the intent is to coverall modifications. aitematives and equivalents falling within the spiritand scope of the invention as defined by the appended claims.

Turning now to the drawings, and at this point especially to FIG. I, itwill be seen that there is a magnetic brush development unit II forapplying toner l2 to a photoconductor 13 on the fly so that any latentelectrostatic images on the photoconductor 13 are developed as it movesthrough a development zone 14. In this instance. the photoconductor i3is coated on a flexible belt 15, but it will be apparent that theprinciples of this invention are equally applicable to development unitsfor drum-type machines. Regardless of the machine configuration, thetoner 12 is typically delivered to the development zone I4 as onecomponent of a developer material 16 which conventionally comprisestriboelectrically charged toner particles bonded to relatively coarse.gran'ular particles of magnetic material. such as ferrite beads.

. In accordance with the present invention. the development unit llincludes a flexible baffle 17 for suppressing uncontrolled emlsslons oftoner 12 while levcling the profile of the developer l6 delivered to thedevelopment zone 1. Otherwise. however. it is essentially the same asthe unit described and claimed in a co-pending and commonly assignedUnited States Patent application filed Jan. l7. 1973. by F.W. Hudsonunder Ser. No. 324,467 on a Toner Preloaded Magnetic Brush DevelopmentSystem."

More particularly, as illustrated, the development unit 11 comprises ahousing 21 which opensoutwardly toward the photoconductively coated sideof the belt 16 to define the development zone 14. inside the housing 21,there-are a plurality-of elongated, permanent magnets 22-26, which aresupported-"within separate non-magnetic, tubular rolls 27-31,respectively, adja-- cent the development zone 14 and in spaced-apartrela'-" tionship along the path of travel of the photoconductor 13therethrough. Each of the magnets 22-26 extends across substantially thefull width of the development zone 14 and is held in a fixed position.Each of the rolls 27-31 also extends across substantially the full widthof the development 'zone 14, but means (not shown) are provided forrotating adjacent ones of them in opposite directions.

in operation. the magnetic field created by the magnets 22-26 entrains aportion of the development material 16 which is nominally stored in asump 32 at the bottom of the housing 21 adjacent the lowermost roll 27.The rotation of the rolls 27-31 causes the magnetically entraineddeveloper material 16 to snake upwardly through the development unit 11so that it is brought into brushing engagement with the photoconductor13 by the rolls 27, 29 and 31. After the developer material 16 passesbetween the photoconductor 13 and the uppermost roll 31, it is releasedfrom the magnetic field so that it drops onto an inclined guide plate 33which returns it to the sump 32 for recirculation. A

To maintain the toner concentration at a suitably high level, there is agenerally conventional toner dispenser 34 mounted on top of the housing21 for adding toner 12 to the partially denuded developer 16 flowingalong the guide plate 33. Most of the additional toner 12 ultimatelybecomes a part of the developer material 16, but some of it tends toremain airborne or to otherwise collect in the toner addition region 35of the housing 21. This collection of free toner 12 is a potentialsource of uncontrolled, powder cloud-like emissions of toner in view ofthe air currents generated by the mpvement of the photoconductivelycoated belt 15, rolls 22-26, and developer 16.

To suppress uncontrolled emissions of free toner, one side of the baffle17 is secured to the interior of the housing 21 slightly forward of thesump 32 and its opposite, free side is biased into engagement with thedeveloper material 16 magnetically entrained on the lowermost roll 27.The baffle 17 extends across substantially the full width of thedeveloper unit 11 to effectively seal the gap between the housing 21 andthe roll 27. if need be, similar baffles may be used to seal other gaps,but this one amply illustrates the invention.

in keeping with one of the more detailed features of this invention, thefree side of the baffle 17 is arcuate so that it presents a continuous,edge free, contact surface for engaging the magnetically entraineddeveloper material 16. Preferably, the baffle 17 is formed from anon-magnetic, resilient material, such as one mil thick brass shimstock, so that it is self-biasing and does not upset the pattern of themagnetic field created by the magnets 22-26. in this instance, thebsflle 17 extends over and outwardly from a metering bar 40 to aid inleveling the profile of the magnetically entrained developer material16, without any significant scraping action. Hence, the baffle 17 sealsagainst the developer material 16 without flicking any significantamounts of the developer out of the development unit 11.

Referring to FIG. 2, it will be apparent that the present invention mayalso be used to advantage in magnetic transport cascade-type developmentunits. The particular development unit 41 selected to illustrate thatincludes a pair of baffles 42 and 43 in accordance with this invention,but is otherwise the same as the unit that is described and claimed in acommonly assigned U.S. Pat. No. 3,641,980 of J. T. Bickmore, whichissuedFeb. 1S, 1972.

More specifically, the development unit 41 comprises a housing 44 whichopens outwardly toward a photoconductively coated drum 45 to define adevelopment zone 46. inside the housing 44, there are two assemblies ofpermanent magnets 47 and 48, which are mounted within separatenon-magnetic, tubular rolls 49 and 50, respectively. For illustrativepurposes, a heavy line has been used to denote the north poles of theindividual magnets of the two assemblies 47 and 48.

The magnetic assemblies 47, 48 and the rolls 49, extend acrosssubstantially the full width of the development zone 46. in operation,the magnetic assemblies 47 and 48 are held in fixed positions, but therolls 49 and 50 are driven (by means not shown) in opposite disectionsso that developer material 51 is magnetically transported from a sump 52in the lower reaches of the housing 44 to a position above a developmentelectrode 53. At that point, the developer 51 is released from themagnetic field and then directed by a guide .plate 54 so that it flowsbetween the photoconductively coated drum 45 and the developmentelectrode 53. Toner is, of course, stripped from the developer material51 as it cascades across the drum 45 to develop any latent electrostaticimage on the photoconductive coating 55. Again, therefore, provision ismade for adding additional toner to the developer material 51 fromtime-to-time. To accomplish that, in this embodiment, there are a seriesof chutes 55 and 56 for guiding the additional toner from a tonerdispenser (not shown) into the sump 52.

In keeping with this invention, the baffies 42 and 43 suppressuncontrolled emissions of toner and level the profile of the developermaterial 51 delivered to the development zone 46. To that end, thebaffle 42 has one side secured to the housing 44 just in front of thesump 52 and its opposite, free side biased into engagement with themagnetically entrained developer material 51 on the lower roll 49. Thebaffie 43, on the other hand, has one side secured to the housing 44 inthe area above the roll 50 and its opposite free side biased intoengagement with the magnetically entrained developer material 51 on theupper roll 50. Both of the baffies 42 and 43 extend across substantiallythe full width of the developer unit 41 and both are preferably formedfrom non-magnetic, resilient material, such as the aforementioned onemil thick brass shim stock. Moreover, the free side of each of thebaffies 42 and 43 is preferably arcuate so that each presents acontinuous edge free, contact surface for engaging the magneticallyentrained developer material 51. in other words, the batfles 42 and 43shown in H6. 2 desirably have the same self-biasing, self-sealing,non-scraping characteristics as the baffle 17 previously described inconnection with FIG. 1. in this embodiment, however, the second baffle I43 is somewhat more important that a correspondingly positioned bafflewould be in the embodiment shown in FIG. 1 because it not only aids insuppressing uncontrolled emissions of toner, but also levels the profileof the magnetically entrained developer material 51 immediately beforeit is released to cascade across the photoconductively coated drum 45.

As best illustrated by FIGS. 3A and 3B, the uniformity of thedevelopment process is improved by leveling the profile of themagnetically. entrained developer material. For example, referring backto FIG. 1 for a moment, there may be substantial variations across thewidth of the development unit 11 in the thickness or pile height of themagnetically entrained developer material 16 on the upstream side of themetering bar 40 and baffle l7 (FIG. 3A). However, the bias acting on thebaffle 17 causes it to redistribute the developer 16 more or Eesslaterally from the higher spots to the lower spots, thereby leveling outthose variations. Consequently, on the downstream side of the meteringbar 40 and baffle 17 (FIG. 38), there is a generally uniformly thicklayer of developer material 16 to be presented to the development zone14.

CONCLUSlON file of the developer delivered to the development zone.

What is claimed is:

l. in a development unit for developing latent electrostatic images on aphotoconductor while said photoconductor is moving through a developmentzone; said unit having a housing, a sump in said housing for storing asupply of developer, means communicating with said sump for adding tonerto said developer, and

means including at least one roll spaced from said housing formagnetically entraining and transporting developer from said sump towardsaid development zone; the improvement comprising a resilient bafflehaving one side secured to said housing and an opposite, free side witha continuous, edge-free arcuate surface biased into engagement with thedeveloper magnetically entrained on said roll. whereby said baffleprovides a seal for suppressing uncontrolled emissions of toner and alsolevels out any variations in the thickness of the developer magneticallyentrained on said roll.

2. The improved development unit of claim I wherein said roll ispositioned to brush the magnetically entrained developer against saidphotoconductor.

3. The improved development unit of claim 2 wherein said baffle isformed from resilient, non-magnetic material and is self-biased to urgesaid surface against developer entrained on said roll.

4. The improved development unit of claim 1 wherein said roll ispositioned to participate in transporting developer from said sump to aposition above said development zone where said developer is released tocascade across said photoconductor.

5. The improved development unit of claim 4 wherein said baffle islocated to engage the developer nearing said position, whereby thevariations in the thickness of the magnetically entrained developer areleveled out just before the developer is released to cascade across saidphotoconductor.

6. The improved development unit of claim 4 wherein said baffle isformed from resilient, non-magnetic material and is self-biased to urgesaid surface against developer entrained on said roll.

7. The improved development unit of claim I wherein said baffle is oneof a plurality of self-biased. non-magnetic baffles positioned tosuppress uncontrolled emissions of toner.

I i i i

1. In a development unit for developing latent electrostatic images on aphotoconductor while said photoconductor is moving through a developmentzone; said unit having a housing, a sump in said housing for storing asupply of developer, means communicating with said sump for adding tonerto said developer, and means including at least one roll spaced fromsaid housing for magnetically entraining and transporting developer fromsaid sump toward said development zone; the improvement comprising aresilient baffle having one side secured to said housing and anopposite, free side with a continuous, edge-free arcuate surface biasedinto engagement with the developer magnetically entrained on said roll,whereby said baffle provides a seal for suppressing uncontrolledemissions of toner and also levels out any variations in the thicknessof the developer magnetically entrained on said roll.
 2. The improveddevelopment unit of claim 1 wherein said roll is positioned to brush themagnetically entrained developer against said photoconductor.
 3. Theimproved development unit of claim 2 wherein said baffle is formed fromresilient, non-magnetic material and is self-biased to urge said surfaceagainst developer entrained on said roll.
 4. The improved developmentunit of claim 1 wherein said roll is positioned to participate intransporting developer from said sump to a position above saiddevelopment zone where said developer is released to cascade across saidphotoconductor.
 5. The improved development unit of claim 4 wherein saidbaffle is located to engage the developer nearing said position, wherebythe variations in the thickness of the magnetically entrained developerare leveled out just before the developer is released to cascade acrosssaid photoconductor.
 6. The improved development unit of claim 4 whereinsaid baffle is formed from resilient, non-magnetic material and isself-biased to urge said surface against developer entrained on saidroll.
 7. The improved development unit of claim 1 wherein said baffle isone of a plurality of self-biased, non-magnetic baffles positioned tosuppress uncontrolled emissions of toner.